Method of chromium plating



United States Patent Ofice 3,393,134 Patented July 16, 1968 3,393,134METHOD OF CHROMIUM PLATING Benno A. Schwartz, Jr., 3278 W. 157th St,Cleveland, Ohio 44111 No Drawing. Filed Mar. 23, 1965, Ser. No. 442,16116 Claims. (Cl. 20416) ABSTRACT OF THE DISCLOSURE A method of repairingdefective areas or spots in chrome plate surfaces in which the area ismechanically cleaned, electrocleaned, electroactivated, electroplatedwith nickel and chromium plated with the use of a hexavalent chromiumplating solution, the electrolytic operations being carried out by brushplating techniques.

This invention relates to the repair of damaged or defective areas ofchromium plated surfaces using socalled brush plating techniques, andmore particularly to methods and solutions whereby damaged or defectivespots or areas of chromium plated articles can be repaired with goodresults and without requiring replating of the entire article.

Heretofore, the spot repair of damaged chromium plated surfaces has notbeen entirely successful. Prior processes and procedures have producedrepaired areas which are more or less detectable to the eye. Among othershortcomings, the color of the repaired surface often failed to matchthe undamaged chromium plated surface, the juncture between the new andold plating was often visible, theadhesion of the plate to theunderlying metal frequently was a problem and the underlying or basicmetal was often not properly protected against corrosion.

A general object of the present invention, therefore, is the provisionof a process whereby a damaged chromium plated surface may be spotrepaired efficiently and at reasonable cost. Another object is theprovision of a process whereby a damaged chromium plated surface may bespot repaired so that the color of the repaired surface matches theundamaged surface. Another object is the provision of a process wherebya damaged chromium plated surface may be spot repaired so that therepaired area is not detectable to the eye under ordinary conditions. Afurther object of the present invention is the provision of a processwhereby a damaged chromium plated surface may be spot repaired usingreadily available equipment and materials and without requiring a highdegree of skill on the part of the operator.

These and other objects are attained using a series of operations orsteps which include electrolytic cleaning, activating and electroplatingwith hand tools which have porous dielectric surfaces that are saturatedwith electrolyte or other solution. Closely adjacent to the poroussurface is an electrode which is in contact with the solution. Theporous surface is then rubbed on the surface to be repaired. Tools ofthis general type are well-known and are widely used in brush platingoperations. The tools may be dipped into the solutions or may beprovided with a chamber connected to a sump or storage tank from whichsolution is pumped. Cleanliness and freedom from particulate matter areimportant to the success of the present process; therefore, thesolutions preferably should be filtered if they are to be recirculated.

The damaged area or part is first straightened, welded, brazed orotherwise repaired as required by the nature of the damage. The area isthen ground away to a smooth surface and polished with a fine abrasiveto a scratch free surface with the various layers of previously appliedelectroplate, such as chromium, nickel and copper on a steel base, wellfeathered in. The surface is then subjected to an electro-cleaningoperation. A hand tool of the type described is connected to a variablevoltage source of DC. that is equipped with a voltmeter and an ammeter,and is made the anode, the object having the damaged surface being thecathode. The hand tool is then rubbed on the damaged surface and beyondthe periphery of the polished area and onto the adjacent originalchromium surface a distance of about two to four inches. The pressure ofthe tool on the surface is light or sof enough pressure being applied toinsure good contact between the tool and the work. The correct pressurecan be determined by watching the ammeter on the power source; with toolittle pressure, the current will be too low and pressure in excess ofthat preferably employed will not cause the current to increase inproportion to the increase in pressure. The electrolyte advantageouslyincludes an alkali metal hydroxide buffered with sodium metasilicate toa pH in the range of from about 9 to about 13 and preferably in therange of from about 10 to about 12. Other alkaline cleaners, such as theproprietary cleaner marketed under the trademark Dalic and identified asNo. 1010, will give excellent results.

The rubbing action is continued until the surface can be rinsed with noWater breaks being visible; that is, the surface is wetted with acontinuous film of the rinsing liquid. The composition of the rinsingliquid advantageously consists essentially of a very dilute solution ofcommercial sulfuric acid in water. The acid neutralizes the alkalinefilm, and freedom from Water breaks gives a clear indication that thesurface is free from grease.

After rinsing, the surface is again subjected to electrolysis, using asimilar hand tool and following generally the same procedure used forthe electro-cleaning, but the rubbing action is not extended quite asfar onto the original chromium plated surface as before. The electrolyteemployed is an acidic solution that is capable of activating the area tobe plated. The activating solution makes the area receptive to plating,probably by eliminating oxides from the surface. The activating solutionpreferably is a solution of sulfuric acid in water, the solutioncontaining much more acid than the rinsing solution.

The rubbing action is continued until a slight haze or change appears onthe original chromium surface that surrounds the polished area. As thishaze develops, there will be a light drag on the tool; the tool will notmove as easily over the surface. The activating operation is thenstopped and the rinsing solution is then used to rinse the surfacethoroughly.

Immediately after the rinsing of the treated or activated area, a layerof nickel is deposited on the surface using a similar hand tool. Therubbing action is similar but is started at preferably the outerperiphery and the entire area to be nickel plated is quickly covered toprevent the surface from becoming passive. This initial operation formsa very thin deposit of nickel and thereafter nickel is deposited only inthe area covered by the initial deposit since the remainder of the areabecomes passive. The rubbing action is kept slightly within theperiphery of the previously activated area. The character of the nickeldeposit is of importance to the success of the process. The depositshould be adherent and substantially free from stress, should initiallypresent a matte appearance and should be soft enough so that it can bebuffed to a high lustre. Examples of appropriate solutions for thispurpose are given later in this specification.

After nickel has been deposited on the surface to the desired thickness(e.g., from 0.0005 to 0.0010" in the areas of thickest deposit) it isbuffed to a high polish using procedures well-known to those skilled inthe art. The direction of the polishing operation should be from thenickel and onto the surrounding chrome to feather out slightly theperiphery of the nickel. In order to minimize the difiiculty ofsubsequently cleaning the buffed surface, heavily greased buflingcompounds should not be employed.

The nickel surface and the immediately adjacent chromium surfaces arethen electrocleaned and electroactivated as before. The cleaning andactivating operations are extended an inch or two onto the chromiumsurface surrounding the nickel and the activation is stopped as soon asthe characteristic haze appears on the chromium and the characteristicdrag on the tool is felt. The area is then immediately rinsed with therinsing solution and then the entire area is immediately swabbed withanother electrode tool that is saturated with the electrolyte that is tobe used in the chromium plating operation, but with the tooldisconnected from the power source. This stops the action of theactivating solution but preserves the activated area in the active stateso that an adherent deposit can be obtained. The electrolyte, asexplained below, contains hexavalent chromium, but is modified from theusual hexavalent chromium electrolyte by the addition of materials tomake it suitable for brush plating operations.

The activated surface is then chromium plated, using the hand tool thatwas employed to swab the area with the chromium plating solution andfollowing the procedure as generally outlined above. The chromiumdeposit is extended beyond the periphery of the nickel deposit and ontothe original chrome, but is stopped a little short of the periphery ofthe activated area. The plating operation is carried out to produce amatte surface chromium coating preferably having a thickness of theorder of 0.000050" to 0.000150". The surface is then washed and thesatin or matte deposit is buffed by conventional means to a high polish.If the work is done correctly, the repaired area will be undetectable,or nearly so, to the naked eye, being substantially undistinguishable incolor and texture from the surrounding original chromium and having goodcorrosion resistance and adhesion.

In order that those skilled in the art may better understand how thepresent invention maybe carried into effect, the following examples aregiven by way of illustration and not by way of limitation. All parts andpercentages are by Weight unless otherwise specified.

A typical automobile bumper having a damaged chromium surface isrepaired as follows:

The bumper is straightened and the damaged surface ground away exposingthe usual nickel or, in some cases, nickel and copper electrodepositsbeneath the electrodeposited chromium and the steel base metal beneaththe K electrodeposits. The grinding leaves a level semi-polished surfaceabout four inches in diameter, for example. The damaged area and theadjacent area of the surrounding chromium are, if necessary, precleanedusing conventional solvents and cleaners and the surface is thenpolished with a series of progressively finer abrasives, up to 400 gritaluminium oxide paper, and a conventional disc type polisher until thesurface to he repaired is substantially scratch-free with layers ofpreviously applied electroplate well feathered in.

The surface is then electrolytically cleaned using a hand toolcomprising a graphite electrode supporting a porous cotton tip aboutthick held in place by cotton gauze. The bumper is made the cathode in aDC. circuit and the tool the anode. The voltage of the power source isadjusted to about 18 volts. The tool is saturated with solution A setforth below and rubbed over the polished surface with a circular motion,starting at the center and working beyond the periphery of thesemipoiished surface about four inches. The rubbing is continued untilthe surface being cleaned is covered entirely with a uniform film ofsolution and no gas bubbles persist or remain on the surface. Thisindicates that the surface is clean. This operation ordinarily requiresabout one minute for the area in question. The average current is about15 amperes and the tool area in contact with the surface is about 5square inches making the cathode current density 3 amperes per squareinch. The amount of current used is about .002 ampere hour per squareinch.

As an example of an alternate Solution A, Dalic 1010 Cleaner, aproprietary solution marketed by The Steel Improvement and Forge Companyof Cleveland, Ohio, may be employed. After the electrocleaning operationhas been continued long enough so that the surface being treated isapparently clean, which ordinarily takes about one minute, the surfaceis rinsed with Solution B given below:

SOLUTION B Sulfuric acid (H 1.84 sp. g.) 6 ml. per liter of finalsolution. Water (H O) To make 1 liter. pH 1.25. Specific gravity 1.0056.

Commercial sulfuric acid and ordinary tap water can be employed.

If the cleaning operation has been carried out satisfactorily, therinsing liquid leaves a thin continuous film with no visible waterbreaks.

After rinsing with Solution B, the surface is activated preparatory toelectroplating with nickel. The activation is accomplished with anotherhand tool having a graphite electrode and porous cotton tip about thick.As before, the tool is the anode and the bumper is the cathode in a DC.circuit. The voltage is about 7.5 volts. The tool is saturated withSolution C below, and rubbed over the surface as before but the rubbingis extended about only 3 inches beyond the periphery of the previouslypolished area. The rubbing is continued until a light haze appears onthe chromium surface adjacent the surface to be replated and adjacentthe area being repaired and until the characteristic drag on the tooldevelops. This ordinarily requires about 30 seconds. At this time, about.1 ampere hour of current has been passed making the amount of currentabout .0013 ampere hour per square inch. The actual current is about 12amperes and the area of electrode tool in contact with the work is about6 square inches resulting in a current density of about 2 amperes persquare inch of tool.

SOLUTION C ml. Sulfuric acid (H SO 1.84 sp. g.) 200 Water (H O) 800 Asbefore, commercial sulfuric acid and tap water can be employed.

At the conclusion of the activating treatment with Solution C, thesurface is immediately rinsed with more of Solution B. Then, withanother tool having a graphite electrode, the previously activated areais plated with a nickel using the following Solution D as theelectrolyte:

SOLUTION D Nickel sulfate (NiSO -6H O) 538 grams per liter. Citric acid(C H O 30 grams per liter. Water (distilled) To make 1.010 liter.

Excellent results also can be obtained using as an alternate Solution Dunder the trade name Dalic Nickel S. The tool is saturated with SolutionD and made the anode in a DC. circuit in which the bumper is thecathode.

The power source is set to about 15 volts and as previously pointed out,the first operation is to rub the tool as rapidly as reasonably possibleover the entire surface to be plated. A soft, circular rubbing action isthen applied starting about one inch beyond the periphery of thepolished area and working toward the center. After the tool has war-med,the voltage may be increased to about 20 volts. The rubbing andelectrodeposition are continued about 20 minutes, the tool is frequentlydipped into the solution to keep it saturated with Solution D. If thevoltage and operation are carried out correctly, a gray or matte satinnickel finish appears. At the completion of the electrolysis, 7 amperehours have been passed in about 20 minutes making the current about .25ampere hour per square inch of plated surface. During most of theelectrolysis, the actual current is preferably about 25 amperes and thearea of the electrode tool in contact with the surface is about 6 squareinches so that the current density is about 4 amperes per square inch oftool.

After the nickel plating has been completed, the surface is then rinsedwith tap water until the electrolyte is removed and then is wiped dry.It is good practice then to test the adhesion of the nickel plate. Thismay be accomplished by firmly sticking a piece of plastic electricaltape across the area that has been replated. After the tape has beenpressed firmly on the surface, it is pulled off sharply at a 90 angle.The tape is then inspected. If any particles of nickel appear in thecenter of the tape over the repaired spot, it indicates that theprocedure has not been carried out properly and the nickel must beremoved by grinding and polishing and the whole process repeated. Ifsmall pieces of nickel appear near the outer edges of the tape where thedeposit is on previously deposited chromium or nickel, thesedifiiculties are probably inconsequential and the non-adhering portionsof the nickel will be removed in the following buffing procedure.However, if the foregoing procedures have been carried out correctly,there Will be little, if any, nickel adhering to the tape when it isremoved.

Assuming that a good deposit of nickel has been obtained, the next stepis to buif the satin-finish nickel to a bright polish. This isaccomplished with a conventional buffing wheel such as a 3" to 5"diameter wheel having a thickness of 1" to 1% that is driven at 2,000rpm. or more by an electric motor. A conventional polishing compound isspread initially on the bumper, the bufling operation is carried outfrom the center of the spot outwardly over the surrounding chromium. Asoft circular motion is employed until the desired highly polishedsurface appears. The outer surface of the wheel must be kept soft andthe Wheel should be periodically cleaned to prevent it becoming loadedwith compound. When the color of the plating is true and all marks havebeen polished out, the bufiing should be completed with a clean wheelthat is passed over the surface in One direction, the movement being inthe same direction as the wheel is turning. Any buffing compound isremoved before the final bufiing, using a clean damp rag.

Next, the area that has been nickel plated and surrounding area of theoriginal chrome are electrocleaned as before using Solution A and rinsedwith Solution B. Then the surface is activated as before with SolutionC, the activating covering over the entire nickel plated surface and theadjacent chromium surface about two inches beyond the periphery of thepreviously ap lied nickel. The activated surface is then rinsed withSolution B and the chromium plating operation started immediately,before the surface has a chance to dry or become passive.

The chromium plating operation is carried out with a 'hand tool similarto those previously described but embodying a lead electrode and apolyester fabric or fiber pad composed, for example, of Dacron, the padbeing about one-half inch thick and covered With a gauze made of apolyester material such as Dacron. Polyester fabrics are employed sincethese materials have good resistance to attack by chromic acid. Cotton,such as used with the other electrolytes, is attacked by chromic acidreducing the hexavalent chromium ions to trivalent chromium whichseriously interferes with the operation of the electrolyte. The tool issaturated with the electrolyte which is Solution E given below, andbefore the tool is connected to the power source and while the surfaceof the work is still wet with solution B, the tool is rubbed quicklyonce over the entire surface that is to be plated, wetting it withsolution E. Then the circuit is completed with the tool the anode andthe bumper the cathode and the power source adjusted for an output ofabout 10 volts. The following electrolyte gives good results:

SOLUTION E Grams per liter Distilled Water, balance.

This electrolyte is of the type disclosed in Belgian Patent No. 632,459of May 16, 1963, with the addition of sodium hydroxide, which isessential for a good brush plating. An alternate solution E is asfollows:

Chromic acid, per liter grams 400 Sodium hydroxide, per liter do 58Sulfuric acid (H SO 1.84 sp. gr.), per liter ml 6 Distilled water,balance.

A satisfactory and in some respects preferred solution E can be preparedutilizing proprietary materials as follows:

Grams per liter Duramir 200 330 Sulfuric acid (H SO l.84 sp. gr.) 0.65Sodium hydroxide 40 Trivalent chromium 5 Distilled water, balance.Duramir 200 catalyst, 19.4 units.

The resulting solution contains hexavalent chromium. The sodiumhydroxide is required to enable the electrolyte to be used in brushplating, to give more uniform color and to prevent spotting.

The rubbing and electroplating operation are continued for about 10minutes, the tool being redipped in the solution to keep the porouspolyester padding saturated. After about 10 minutes, a characteristicgray satin or matte finish appears. At this point, 5.0 ampere hours havebeen passed making the amount of current about .10 ampere hour persquare inch. The actual current during the electrolysis is preferablyabout 40 amperes. In the chromium plating, the area of the electrodetool in contact with the surface is about 8 square inches and thecurrent density about 5 amperes per square inch. It is desirable toreduce the voltage at the end of the chromium plating operation to about5 volts and make a final pass with the tool around the periphery of thechromium deposit. This is the area where a ring that is visible beforebutting develops and the final low-voltage pass decreases the darknessof the ring and reduces the amount of buffing required to eliminate it.

The chromium plate is rinsed thoroughly with tap water, wiped dry with aclean rag and buffed to a highly polished bright surface. The buffing isfrom the center outward, blending the new chromium plate with theundamaged chromium plate. The color of the repaired area matches that ofthe remainder of the chromium surface and if the operations are properlycarried out, the repaired area is not readily detectable by visualinspection.

As mentioned above, so far as I am aware, it has not been possibleheretofore to make satisfactory spot repairs or secure proper adhesionon the chromium and the repaired area was always readily visible to thenaked eye. Various factors contribute to the success of the presentprocess. Attention is directed particularly to the followmg:

The preliminary preparation of the surface is important. Theelectrolytic cleaning operation is preferably carried out using asolution with alkali metal ions and the cleaning' is extendedsubstantially beyond the area of the repair. While alkali metalhydroxides are preferably employed, other cleaning solutions known tothose skilled in the art may be used. The activating solution is ofparticular importance. While steel, nickel and copper surfaces are notdifiicult to plate, the activation of the surrounding chromium surfaceso that it will receive adherent plated coatings and so that the finalchromium plate will blend into the original chromium plate is of greatimportance. This is carried out, as explained above, with a solutioncontaining sulfuric acid preparatory to both the nickel and chromiumplating steps. In both cases, the activating is kept to a minimumconsistent with the desired result so that the original chromium platingsurrounding the area that is repaired will not be damaged but will bemade receptive to subsequent chromium plating. It is also to be notedthat the plating takes place immediately, while the surfaces to beplated are still wet with the slightly acidic rinse.

The character of the nickel deposit is also of importance. A nickelsolution is required that can be used as a brush plating solution andthat will give dense, adherent deposits that are soft and relativelyfree from stress. It is important that the deposits be adherent and freefrom stress, otherwise cracks or peeling will develop and the underlyingmetal will corrode in service. Soft deposits are in general freer fromstress than hard deposits and furthermore, the soft deposits are easierto buff to the desired polish and to feather into the surrounding andunderlying original chromium.

A factor of controlling importance is the use of hexavalent chromiumsolutions in the process. Heretofore, so far as I am aware, hexavalentchromium solutions have not been used successfuly for brush plating,although hexavalent solutions are customarily used in tank plating.According to the present invention, known hexavalent chromium solutionsare modified so that they can be used in brush plating; the resultantdeposits are adherent and dense and have a good color match with thesurrounding previously plated chromium that in all probability wasproduced by immersion plating, using a hexavalent chromium solution. Theaddition of sodium hydroxide to the hexavalent chromium solutions makesthem suitable for brush plating. It is also important to DC. sourcehaving a low A.C. ripple factor in carrying out the chromium platingoperation. Furthermore, the brush plating tool should be made with anabsorbent material that will not contaminate the chromium solutions. Itis for this reason that polyester materials are preferably used, sincethese materials are inert to the plating solution. If cotton, which isentirely satisfactory for the other solutions, were employed, thereaction between the electrolyte and the cotton would result in theintroduction of an excess of trivalent chromium into the solution andreduce the effectiveness of the chromium plating operation. The voltagesand currents employed give a matte surface chromium deposit which iseasily buffed to a bright condition that matches the originally platedchrome and which is more adherent and freer from cracks than brightdeposits of chromium.

In carrying out the entire operation, it is desirable to keep thesolutions free from particulate matter and other contaminants, and whilethe work is often done under adverse conditions in the ordinaryautomobile shop, efforts should be made to keep the solutions and toolsclean and to avoid mixing and contamination.

Another characteristic feature of the present invention is the extent ofthe areas which are mechanically ground and polished, electrocleaned,electroactivated and electroplated. The area which is mechanicallyground and polished of course encompasses the damaged area that is to berepaired and goes far enough beyond the damaged area so that the variousexisting layers may be feathered into each other. Thus, the center maybe bare steel surrounded by copper (if the original part embodied anelectroplated copper substratum), then nickel and finally the originalchromium plate. This mechanically polished area is plated with nickeland the nickel is extended slightly over the original chromium plate.The final chromium plating covers all of the nickel and extends slightlyover the original chromium plate so that it can be blended into theoriginal chromium.

In carrying out the electrolytic operations, the area which iselectrocleaned is the greatest, extending substantially beyond theperiphery of the mechanically polished area onto the undamaged chromiumsurface for a distance of, for example, 3" to 6". The area which isactivated to receive the plating is extended beyond the periphery of theoriginal mechanically polished surface but preferably stops 1 to 1 /2inches short of the periphery of the cleaned area. The electrodeposit ofnickel extends beyond the periphery of the semi-polished surface ontothe undamaged surrounding chromium surface that has been activated butpreferably not more than about 1 to 1 /2 inches onto the chromium. Thechromium deposit covers significantly beyond the nickel, preferably 1 to1% inches. The chromium deposit should not extend beyond the activatedarea and preferably is kept about 1 inch short of the boundary of theactivated area.

The conditions employed in carrying out the electrolytic operations maybe varied within reasonable limits and permit the use of readilyavailable equipment. However, as previously noted, the power supplyshould have a low A.C. ripple content, preferably less than 15% andadvantageously about 4%. Advantageously, the entire process is carriedout without the application of heat other than that developed during theoperation. The solutions may be kept at normal room temperatures,preferably at temperatures in the range of from about 50 F. to about F.During the electrolysis, there is a noticeable elevation in temperatureby the flow of electric current, particularly during the nickeldeposition. The temperature of the electrolyte may rise to as high as200 F. increasing the conductivity of the electrolyte and thepermissible maximum current densities, thus permitting acceleration ofthe deposition of the nickel.

The voltage of the source should be adjustable from about 5 volts toabout 30 volts. In the case of the nickel plating, the nickel beginsburning at progressively lower current densities with progressivelylower temperatures. This effect is predominant over the effect oftemperature on current density. In practice, therefore, the nickelshould be started at lower voltages when the temperature is lower. Whenthe conductivity of the solution is low because of low temperatures, itmay be desirable for the cleaning and activating and chromium platingoperations to use higher voltages initially than those specifiedheretofore in order to force sufficient current through the electrolyteto start the electrolysis. This is well known to those skilled in theart.

The optimum operating current densities for carrying out theelectrolysis for each of the steps of the process are of the order ofthe current densities heretofore set forth. Preferably, the currentdensity for effectively electrocleaning the surface is in the range of aminimum of about 2 amperes per square inch of tool surface. The maximumis limited only by the heating effect on the electrolyte. The amount ofcurrent ordinarily necessary for cleaning depends on the degree ofcleanliness of the original surface but it is at least .003 ampere hourper square inch for an apparently clean surface.

The current densities preferably used for activating are preferably inthe range of from about 1 ampere per square inch to about 3 amperes persquare inch of tool surface. The amount of current usually necessary foractivating is about .001 ampere hour per square inch. Too much or tooprolonged activating removes chromium from the surface without anyadvantage and in fact with some disadvantages. Therefore, the activationshould be stopped as soon as the characteristic haze appears on thechromium surface.

In the electrodeposition of nickel, electrolyte temperatures of 130 to190 F. and higher current densities short of the point of burning areadvantageously used. Heat develops quickly during the nickel plating andthe heat developed from the current is generally adequate. When thesolution and part are cold, current density preferably should not behigher than about 2 amperes per square inch of tool. When a temperatureof about 130 F. or higher is reached, the current density can range from3 to 8 amperes per square inch of tool area. Preferably the currentdensity should be in the range of from about 4 amperes per square inchto about 6 amperes per square inch of tool area during the major portionof the plating operation. The thickness of the nickel layer should bekept bet-Ween 0.0005 inch and about 0.0015 inch for best results. Theamount of current required for such thicknesses of nickel is in therange of from about .125 ampere hour per square inch to about .375ampere hour per square inch.

In depositing chromium, the preferred current densities are in the rangeof from about 2 amperes per square inch to about 10 amperes per squareinch of tool area. Preferably, the chromium is deposited with currentdensities in the range of from about 3 amperes per square inch to about6 amperes per square inch. The thickness of the chromium layer ispreferably in the range of from about 0.000050 inch to about 0.000150inch. The amount of current necessary for obtaining thicknesses in thisrange is from about 0.05 ampere hour per square inch to about 0.15ampere hour per square inch. Greater thickness of chromium does notimprove the final result and costs more in plating and buffing time.

The hand tools used for carrying out the present process are well knownto those skilled in the art. Generally, the tools include anodes whichare for all practical purposes inert and insoluble in the electrolytesolution with which they are to be used. For the electrocleaning,activating and the electrodeposition of nickel, the anode preferably iscomposed of graphite. Other materials, however, such as, for example,platinum, platinum on titanium or atntalum, rhodium on titanium ortantalum, or lead may be used. For the electrodeposition of chromium,the anode is preferably made from lead. Graphite, carbon, platinum,platinum on titanium and the like, however, may be substituted. Theworking area of the electrode preferably is about 4 to 10 square inches.For the electrocleaning, activating and nickel plating operations, theporous absorbant material is preferably cotton batting held in place bycotton gauze. For electroplating of chromium, a polyester fiber battingsuch as Dacron held in place by a polyester gauze is employed.Undoubtedly, other materials that are inert to the various electrolytescould be used with success.

The tools preferably are moved at speeds of about 4 to 10 inches persecond during the various operations, and are kept well saturated withthe several electrolytes by frequent dipping into the supplies. Currentdensities can be increased with more rapid movements of the tools.

While preferred embodiments of the invention have been disclosed, othermodifications and variations thereof are undoubtedly possible. The scopeof the invention is defined by the appended claims.

I claim:

1. A method for repairing a defective area in a chromium plated sufacewhich includes, in order, the steps of mechanically grinding andpolishing the surface to remove the defective plating in the area to berepaired, electrocleaning the defective area and the surroundingoriginal chromium plated area by means of a brush plating tool, the toolthe anode and the surface the cathode, electroactivating theelectrocleaned surface by means of a brush plating tool with the toolthe anode and the surface the cathode, electroplating nickel on theactivated area by means of a brush plating tool, the nickel platingextending over the previously damaged surface and onto the surroundingoriginal chromium area, polishing the electrodeposited nickel,electrocleaning and electroactivating the nickel deposit and thesurrounding chromium area as before, and chromium plating the nickeldeposit and the immediately surrounding activated area of the originalchromium by a brush plating operation employing a hexavalent chromiumplating solution, and finally polishing the chromium deposit.

2. A method according to claim 1 wherein the activating solutionconsists essentially of a solution of sulfuric acid in water.

3. A method according to claim 2 wherein the activating solutionconsists essentially of a solution of 200 ml. per liter of sulfuric acidof 1.84 specific gravity in water.

4. A method according to claim 1 wherein the cleaning is carried outwith a solution consisting essentially of a solution of sodium hydroxideand sodium metasilicate in water.

5. A method according to claim 1 wherein the nickel plating is carriedout with a solution consisting essentially of nickel sulfate, citricacid and water.

6. A method according to claim 1 wherein after the electroactivatingoperations and prior to the nickel plating and chromium platingoperations, the surface is rinsed with :a dilute acidic solution.

7. A method according to claim 6 wherein the dilute acidic solutionconsists essentially of 6 ml. per liter of sulfuric acid of 1.84specific gravity in water.

8. A method according to claim 1 wherein the hexavalent chromiumsolution contains sodium hydroxide.

9. The method of brush electroplating a chromium surface with anadditional adherent deposit of chromium which includes the steps ofelectroactivating the previously deposited chromium surface with asolution of sulfuric acid employing a brush plating tool in which thebrush plating tool is the anode and the work the cathode, rinsing thesurface with a dilute solution of sulfuric acid and brush plating acoating of chromium over the activated surface using a solutioncontaining as essential ingredients hexavalent chromium, sodiumhydroxide and sulfate ions.

10. The method according to claim 9 wherein the electroactivatingoperation is stopped substantially as soon as a haze appears on thesurface of the previously deposited chromium.

11. The method according to claim 10 wherein the surface to be chromiumplated is swabbed with the chromium plating electrolyte immediatelyafter activating and rinsing and the brush electroplating operation isstarted immediately thereafter.

12. The method according to claim 11 wherein the tool is connected to aDC. source having less than 15% AC. ripple.

13. The method according to claim 12 wherein the voltage is about 10volts and the current density about 5 amperes per square inch of toolarea.

14. The method according to claim 13 wherein the brush plating toolembodies an absorbent pad composed of polyester fibers.

15. A process for repairing a defective area in a chromium platedsurface of an object which comprises in sequence:

(1) grinding said defective area to expose a semipolished underlyingsurface;

(2) electrocleaning said semi-polished surface and the surrounding areaby making said surface the cathode in an electric circuit, providing ananode, spacing said anode from said surface, maintaining a porousdielectric material between and touching said surface and said anode,saturating said material with an alkaline aqueous solution, and rubbingsaid surfce with said porous material whereby said solution is subjectedto electrolysis at said surface;

(3) rinsing said surface with a weakly acidic solution;

(4) activating said surface and the surrounding area by making saidsurface the cathade in an electric crcuit, providing an anode, spacingsaid anode from said surface, maintaining a porous dielectric materialbetween and touching said anode and said surface, saturating said porousdielectric material with an activating solution consisting essentiallyof an aqueous solution of sulfuric acid, and rubbing said surface withsaid porous material;

(5) rinsing said surface with said weakly acidic solution;

(6) electrodepositing nickel on said surface and the immediatelyadjacent chromium area by making said surface the cathode in an electriccircuit, providing an anode, spacing said anode from said surface,maintaining a porous dielectric material between and touching said anodeand said surface, saturating said porous dielectric material with anaqueous solution containing nickel ions and rubbing said surface withsaid porous material whereby a layer of nickel is deposited on saidsurface;

(7) rinsing said surface with water;

(8) drying said surface of said nickel layer;

(9) bufiing said surface of said nickel layer to a bright finish;

(10) electrocleaning the surface of said nickel layer using theprocedure of step 2;

(l1) rinsing said surface of said nickel layer with said weakly acidicsolution;

(12) activating said surface of said nickel layer and a portion of thesurrounding chromium using the procedure of step 4;

(l3) rinsing said activated surface with said weakly acidic solution;

(14) electrodepositing chromium on said surface of said nickel layer andthe immediately surrounding chromium by making said surface the cathodein an electric circuit, providing an anode, spacing said anode from saidsurface, maintaining a porous dielectric material between and touchingsaid anode and said surface of said nickel layer, saturating said porousmaterial with a hexavalent chromium plating solution, and rubbing saidactivated surface of said nickel layer and the surrounding chromium withsaid porous material whereby a layer of chromium is deposited;

(15) rinsing the surface of said chromium layer;

(16) drying said chromium layer; and

(17) buffing said surface of said chromium layer to a bright finish.

16. A process for repairing a defective area in a chromium platedsurface which comprises:

(1) mechanically grinding and polishing the surface to remove thedefective plating in the area to be repaired;

(2) electrocleaning the defective area by means of a brush plating toolcomprising a graphite electrode and an absorbent porous dielectricmaterial, making the tool the anode in a DC. circuit, making the surfacethe cathode in the circuit, substantially saturat- 2 amperes per squareinch of tool surface in contact with the work, the rate of rubbing beingin the range of from about 4 inches per second to about 10 inches persecond;

(3) rinsing said surface with an aqueous solution consisting essentiallyof about 6 ml. per liter of commercial sulfuric acid and the balancewater;

(4) electroactivating the electrocleaned surface using the procedure ofstep 2 but employing a solution consisting essentially of about 200 ml.commercial sulfuric acid having a specific gravity of 1.84 and 800 ml.of water, and stopping the activation when a haze appears on thechromium area surrounding the defective area;

(5) rinsing as in step 3;

(6) immediately electroplating nickel on the major portion of theactivated area using the procedure outlined in step 2 but with asolution consisting essentially of about 538 grams per liter of nickelsulfate (NiSO -6H O), and 30 grams per liter of citric acid, the currentdensity being in the range of from about 3 to about 4 amperes per squareinch of electrode surface, rubbing the tool over the defective area anda portion of the activated area of chromium surrounding the defectivearea but stopping the tool short of the periphery of the activated areaand providing a nickel deposit having a thickness of from about 0.0005"to about 0.0010" having a matte appearance;

(7) rinsing the resultant nickel deposit with water;

(8) drying the nickel deposit;

(9) bufling the nickel deposit until it has a polished surface;

(10) electrocleaning the nickel surface as in step 2;

(11) rinsing as in step 3;

(12) electroactivating the nickel surface and the surrounding chromiumsurface for a distance of about 2 to 3 inches beyond the periphery ofthe nickel deposit as in step 4;

(l3) rinsing as in step 5;

(l4) electroplating chromium using the procedure outlined in step 1 butwith a solution containing as essential ingredients hexavalent chromium,sodium hydroxide and a small amount of sulfate ions, the rubbing actionof the tool being extended beyond the periphery of the nickel platedarea a distance of from about 1 inch to about 1 /2 inches but stoppingshort of the periphery of the activated area;

(15) rinsing the resultant chromium deposit as in step 7; and

(16) bufiin-g said chromium deposit.

References Cited UNITED STATES PATENTS 2,046,440 7/1936 Adey 204--l52,118,956 5/ 1938 Wagner 204-32 2,145,518 l/1939 Lindh 20436 2,965,55112/1960 Richaud 204-32 2,992,171 7/ 1961 MacLean 20432 3,313,715 4/1967Schwartz 204-15 FOREIGN PATENTS 848,585 9/ 1960 Great Britain.

OTHER REFERENCES Polishing and Bufiing for Chromium Plating, Eldridge,C. H., Metal Industry, vol. 26, No. 6, June 1928, pp.

The Effects of Various Surface Treatments in Cleaning and Preparing,Copper, Nickel and Steel for Chromium Plating, Metal Finishing, August1946, pp. 340-345.

JOHN H. MACK, Primary Examiner.

HOWARD S. NVILLIAMS, Examiner.

T. TUFARIELLO, Assistant Examiner.

